1. Field of the Invention
This invention relates to angular velocity sensors, and particularly to an angular velocity sensor (e.g., a gyro sensor, yaw rate sensor), which can detect Corioli's force that acts on a movable portion provided on a substrate along a flat plane parallel to the substrate when angular velocity is generated about an perpendicular axis of the substrate as a result of oscillation of the movable portion.
2. Related Art
Conventionally, capacitance detection type angular velocity sensors have been used for vehicles, arcade games and so on, and have been developed to further downsize so as to reduce mounting space or cost. However, output signals based on capacitance changes due to an action of the angular velocity necessarily becomes small, since a capacitance detection portion is downsized. It is difficult to design a processing circuit to accurately take out only desired signals from such small output signals with removing noise.
This kind of angular velocity sensor is disclosed in JP A 8-220125. This conventional angular velocity sensor has two oscillatory masses (oscillators) that oscillate in opposite phases each other in a frame and an evaluation unit that processes measured signals from the angular velocity sensor. The evaluation unit filters out disturbance generated by the oscillatory masses. This conventional angular velocity sensor can output signals based on substantially twice capacitance changes and can remove the noise relatively easily.
However, according to the conventional angular velocity sensor, since the oscillatory masses having rectangular-shape are merely arranged in parallel to each other, a size of total angular velocity sensor tends to become bulky. Hence, it is inadequate from a downsizing standpoint.
In this conventional angular velocity sensor, it can be thought to further add the oscillatory masses to further enlarge the measured signals from the angular velocity sensor for the purpose of improving an S/N ratio (signal/noise ratio).
However, the mere addition of the oscillatory masses may cause inconveniences that the size of total angular velocity sensor becomes further bulky, and that the noise may not be adequately removed.